Clandestine relationships are at the heart of his latest movie, Snow Flower and the Secret Fan, an epic about the new and old China starring two of Asia’s most famous actresses—South Korea’s Gianna Jun and China’s Li Bing Bing. Based on the international best-seller by Lisa See, the film explores the traditional bond of laotong, in which two young girls would pledge eternal sisterhood.

After falling in love with the book (“It made me cry,” she says), Suzhou-born Wendi Deng Murdoch set about producing it with her writer friend Florence Sloan, who also has Chinese roots. The two gravitated to Wang (The Joy Luck Club, Maid in Manhattan), a filmmaker known for his deft touch with women’s stories. But where See’s novel takes place in the 1800s, Wang wanted to show what’s happening in China right now. At his suggestion, the movie interweaves See’s original story with one set in present-day Shanghai.

Li stars as Nina, a financial hotshot who’s about to be transferred to New York when she hears about an accident involving her estranged best friend, Sophia (Jun), an artistic soul whose life is as chaotic as Nina’s is controlled. Investigating what happened to her onetime friend, Nina stumbles across a manuscript that tells the story, in nineteenth-century Hunan, of two young friends, Lily and Snow Flower, who sign a laotong pact and send secret letters written on fans. Where the pragmatic Lily (also played by Li) becomes the wife of an emotionally distant rich man, her dreamy “little sister” (Jun again) winds up married to a coarse country butcher. As it hopscotches between the mucky Hunan countryside and today’s shiny, skyscrapered Shanghai (glamorously shot by Richard Wong), Snow Flower sometimes loses its way—you’re not quite sure whether you’re watching a Chinese tearjerker or a Western art movie. But one thing is sure. The movie provides a fine showcase for its lead actresses, both superb, who deserve to be better known here.

From the moment we meet in the bar of their Manhattan hotel, I’m struck by how fittingly they were cast. Where the petite, poised Li Bing Bing is focused like a laser, Gianna Jun is lanky, shy, and relaxed—she does the interview sans makeup in her robe.

“Gianna’s strength,” says Wang, “is that she’s always very real and natural—no false moves.” Indeed, on-screen and off-, the 29-year-old Seoul native has a disarming openness that explains her easy rise to stardom. Discovered by a fashion editor at seventeen, she started out modeling but soon turned to acting. By 20 she had starred in the hit love story Il Mare (remade as The Lake House with Sandra Bullock) and soon after did My Sassy Girl (also remade by Hollywood), a crazy romantic comedy that did for her what Pretty Woman did for Julia Roberts.

If Jun has the inviting appeal of a romantic lead, her costar bristles with the confident physicality you might expect of one whose mother performed in kung-fu opera. Although Li won the Chinese-language equivalent of the Best Actress Oscar for the World War II drama The Message, she’s best known for entertaining action pictures like Detective Dee and the Mystery of the Phantom Flame (opening in the U.S. this fall) and The Forbidden Kingdom, in which she played a sword-wielding demon. She loves making those kinds of films, but she appreciated the chance to do something different in Snow Flower. “The emotions are more subtle,” she says.

The wildly different stars wound up forging their own particular version of laotong. “I didn’t realize she’d be such a great actress,” Jun tells me, “and now it’s like we’re sisters.” Li nods happily. “Making this movie,” she says, “was like a love affair.”